SCBWI: the blog - If you are a children's book writer (picture book, MG or YA) you have to know the SCBWI organization. Their sole existence is to help writer's succeed. The very charming and talented Lee Wind blogs for SCBWI. Blog posts are informative pieces about quality writers and illustrators that truly enrich children's publishing.
Literary Rambles - If you don't recognize these two faces, then you're in the wrong business. Casey and Natalie run the Literary Rambles blog. Giving you AMAZING in depth data on agents. (Your number one source when querying.) And just like their blog promises they are "Spotlighting Children's Book Authors, Agents, and Publishing."
Jane Friedman - Jane (and her team of bloggers) have great advice on how to refine the craft of writing and how to navigate the publishing industry. They give in-depth breakdowns of various aspects that go into writing a novel but in a logical and simplistic way. This blog can really help you tackle some of the tougher issues in your writing.
Nathan Bransford - Once an agent, now a successful MG author. Not only are his archives full of juicy goodness for a writers but his current posts continue to give solid writing advice and discuss the current issues affecting the ever-changing publishing industry.